Method and apparatus for cleaning interengaging stretch rollers

ABSTRACT

To clean a pair of counterrotating stretch rollers having surface formations that interengage and that stretch a laminate web transversely to a travel direction in which the web passes between the interengaging rollers gas streams carrying dry-ice particles are directed at surfaces of the counterrotating rollers such that the particles free contaminants from surfaces of the rollers. The freed contaminants and dry-ice particles are aspirated from immediately adjacent each of the rollers while the rollers are rotating and, in fact while the production operation of the web is taking place.

FIELD OF THE INVENTION

The present invention relates to interengaging stretch rollers. More particularly this invention concerns a method of and apparatus for cleaning such rollers.

BACKGROUND OF THE INVENTION

In the manufacture of a stretchable laminate as defined in U.S. Pat. No. 6,281,610, two nonwoven layers are bonded to the opposite faces of an stretchable normally plastic-film core to form a three-layer web. This web is then pulled in a web-travel direction through the nip between a pair of counterrotating stretch rollers rotatable about respective axes flanking and perpendicular to the web-travel direction. Each web forms a plurality of axially spaced ridges or disks separated by radially outwardly open gaps or grooves, with the rollers interengaged with the ridges of each roller fitting in the grooves of the other roller, but with a slight all-around spacing. Thus as the three-layer web is pulled through it is stretched transversely to the web-travel direction, normally somewhat beyond the elastic limit of the nonwovens so that they are permanently stretched. The end product is a laminated textile web that has many uses, particular those uses demanding durability and water-absorbing capacity.

Deposits of contaminants mainly constituted by bits of the fibers of the nonwoven layers and the adhesive bonding the nonwovens to the cure plastic film end up on the surfaces of the stretch rollers. They can impede the stretching process and also damage or at least soil the web being manufactured. In order to remove these deposits, it is necessary to stop and mechanically clean the system. Valuable production time is lost by this stoppage of the system. Furthermore, labor costs are incurred for cleaning.

In general, cleaning processes using dry-ice particles have been known for many years. Thus, for example, special mobile apparatuses are used for blast cleaning with dry ice. This is a compressed-air blast method in which dry ice is used as a blast cleaning abrasive.

Dry ice is solid carbon dioxide that under normal conditions changes at −78.48° C. directly from solid to gas without passing through a liquid phase, the solid-to-gas process being known as sublimation and the gas-to-solid process as deposition.

U.S. 2009/0032993 describes a casting roller with a smooth surface to which a liquid polymer mass is applied. The polymer film is subsequently detached from the roller. A cleaning of the smooth surface of the casting roller is carried out by blowing-on dry-ice particles. Blast-cleaning with dry ice is also used to clean yarn filament transport rolls in JP 7186048, and U.S. 2012/0007060 describes the removal of adhesive residue on release liners by abrasive particles that can be dry-ice particles. Finally it is known from DE 10 2009 043 033 to clean rolls and rollers in casting systems, rolling mills or strip processing lines for metal strips with dry ice. The cleaning can be carried during a rolling operation. The apparatus used for this purpose is positioned at a minimal spacing from the cylindrical surface of the rollers or rolls to be cleaned and is pushed along the roll body or roller body. The apparatus is not suitable for profiled stretch rollers.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved method of and apparatus for cleaning stretch rollers used in the manufacture of laminated webs.

Another object is the provision of such an improved method of and apparatus for cleaning stretch rollers used in the manufacture of laminated webs that overcomes the above-given disadvantages, in particular where the production system does not need to be stopped and the contaminants can be reliably removed during the running stretching process.

SUMMARY OF THE INVENTION

To clean a pair of counterrotating stretch rollers having surface formations that interengage and that stretch an elastic laminate web transversely to a travel direction in which the web passes between the interengaging rollers gas streams carrying dry-ice particles are directed at surfaces of the counterrotating rollers such that the particles free contaminants from surfaces of the rollers. The freed contaminants and dry-ice particles are aspirated from immediately adjacent each of the rollers while the rollers are rotating and, in fact while the production operation of the web is taking place.

The dry-ice particles striking the surface of the stretch roller abruptly supercool the contaminant deposits. Since the deposits have a different coefficient of thermal expansion from the surfaces of the rollers, thermal stresses occur that lead to microcracking in the contaminant layer. Pulverized dry-ice particles penetrate into the microcracks and sublime. The contaminants are detached from the surface as a result of the abrupt volume increase during sublimation. The detached contaminant and excess dry ice are aspirated.

With the method according to the invention, the technique of blast cleaning with dry ice is integrated into a running incremental stretching process for activating an elastic laminate and used thereby to clean interengaging, rotating stretch rollers on the fly, that is without shutting down the is production operation. This represents a considerable technical advance compared to stretching methods according to the prior art, since the production system no longer has to be stopped for cleaning. Productivity is substantially increased by the integration of a cleaning unit into the production system. Since the articles produced by the application of the stretching process are mass-produced articles such as elastic tapes for baby diapers, for example, this leads to a considerable saving in terms of operating costs. What is more, the rollers do not pass cyclically through clean and dirty phases in which products of different quality are produced, but instead can be continuously maintained at a high degree of cleanliness.

Surprisingly, blowing dry-ice particles leads to very good cleaning effects of the stretch rollers, although the surfaces thereof are heavily profiled. This is surprising, since the high raised formations and deep recessed formations make a uniform distribution of the dry-ice particles on the surface difficult. An application of blast cleaning with solid carbon-dioxide particles of heavily profiled surfaces during a running production operation has not hitherto been considered.

The dry-ice particles are blown onto the surface by respective nozzles, with at least one nozzle assigned to each stretch roller. In order to achieve a distribution of the dry-ice particles on the surface of the stretch rollers that is as uniform as possible despite the raised formations and recessed formations, the dry-ice particles are preferably blown onto the surface by a nozzle that is moved with a traversing or reciprocating control movement parallel to the rotation axis of the stretch roller past its raised and recessed formations. The nozzle can be connected to an actuator connected to a controller designed to shift the nozzles at periodic intervals at a predetermined speed along the surface and to blow out dry-ice particles while moving.

With another variant of the invention a plurality of nozzles are arranged next to one another parallel to the rotation axis of each stretch roller ensure uniform distribution of the dry-ice particles.

It has proven to be particularly advantageous if the angle at which the dry-ice particles strike the surface can also be varied by an actuator. The controller can control this operation such that, as the nozzle moves parallel to the rotation axis of the stretch roller, the blast angle of the nozzle is varied.

Furthermore, it has proven to be advantageous if the spacing between the nozzle and the surface can be varied by the actuator.

To aspirate the contaminant particles detached from the profile surface of the stretch rollers, a aspirator can be used that operates at subatmospheric pressure and preferably has an suction slot or port downstream of the nozzles with respect to the rotation direction of the respective stretch roller. Impairment of the stretching process and consequently also of the production process in the manufacture of activated elastic material webs is avoided by the suctioning-off of the removed contaminant and the gaseous carbon dioxide or residual not yet sublimed dry-ice particles.

The dry-ice particles are blown by a stream of carrier gas onto the surfaces of the stretch rollers. Air is particularly suitable as a stream of carrier gas here. With certain applications an inert gas can also be used as a carrier gas, such as nitrogen or carbon dioxide, for example. In this case the carrier gas is supercold, that is at a temperature below the freezing temperature of carbon dioxide, and the particles are generated immediately upstream of the nozzle by adding gaseous carbon dioxide to the supercold carrier gas. This way the formation of the dry-ice particles takes place in the nozzles.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. is a partly schematic diagram for the production of a film laminate using an incremental stretching process with integrated dry-ice cleaning; and

FIG. 2 is a perspective view of two interengaging stretch rollers with integrated dry-ice cleaning.

DETAILED DESCRIPTION

As seen in FIG. 1 a film strip 1 of an elastomeric polymer is bonded between two layers of a nonwoven 2 by adhesives 3 in a laminator 4. Subsequently, the material web 5 is stretched by a stretcher 6. The stretcher 6 comprises two interengaging stretch rollers 7 that are driven for counterrotation by drive means illustrated schematically at 16 (FIG. 2) to pull the web 5 through in a web-travel direction D shown vertical in FIG. 1 and horizontal in FIG. 2.

Dry-ice particles 9 are blown by a stream 10 of carrier gas onto the surfaces of the stretch rollers 7 by respective nozzles 8. The detached contaminants are aspirated by the is respective aspirators 11. One nozzle 8 and one aspirator 11 are juxtaposed with each stretch roller 7.

FIG. 2 is a perspective view of the two stretch rollers 7. The stretch rollers 7 are each formed by a plurality of identical circular disks 13 separated by radially outwardly open gaps or grooves 14. The disks 13 of each roller engage with play in the grooves 14 of the other roller 7, so that the rollers mesh or interengage, normally without touching. As the web 4 is pulled through them in the travel direction D, it is inherently stretched perpendicular to this direction D as is well known in the art.

For clarity of view, FIG. 2 shows only the nozzle 8 and the aspirator 11 of the upper stretch roller 7. Stretching of the laminate takes place transversely to the web-travel direction as mentioned above. A stretcher 6 of this type is therefore also referred to as a CD (cross-direction) stretcher

The aspirators 11 each have an elongated mouth or port open radially inwardly at the respective roller 7 and extending parallel to the rotation axis thereof generally the full axial length of the roller 7. In this manner any particles of dry ice or fibers are removed from the site here to avoid reintroducing them into the web 5 or dirtying the surrounding work area.

The dry-ice particles 9 are blown by the nozzles 8 onto the surfaces of the stretch rollers 7. The particles may be made as shown in FIG. 1 by using nitrogen from a supply 19 at a temperature below the freezing point of carbon dioxide as the carrier gas and mixing gaseous carbon dioxide from a supply 18 with it right at each of the nozzles 8. Each nozzle 8 can be shifted by an actuator 15 parallel to a rotation axis 12 of the respective stretch roller 7. The actuator 15 are each connected to a controller 17 that moves the respective nozzles parallel to the rotation axis 12 at specific time intervals at a movement speed stored in the controller 17 so as to reciprocate the nozzle 8 axially back and forth along the respective roller 7. The contaminants removed are drawn off by the aspirators 11 and therefore do not interfere with the production operation.

The rollers 7 thus radially overlap or interengage at an inner side and the respective nozzles 8 and aspirators 22 are radially closely juxtaposed with diametrally opposite outer sides of these rollers 7. Relative to the rotation direction of each roller 7, the nozzle 8 is upstream of the respective aspirator 11 so that the outer surface of each roller 7 is swept by the nozzle 8 to direct the dry-ice particle 9 at the outer side, where they free up contaminants on the surface that are then sucked in by the respective aspirator 11. In this manner the rollers 7 are cleaned on the fly, on the one inner side doing their job of stretching and texturing the web 5 while their opposite outer sides are being cleaned. In this manner a steady state of cleanliness can be maintained, ensuring that the product produced is of very uniform quality. 

We claim:
 1. A method of cleaning a pair of counterrotating stretch rollers having surface formations that interengage and that stretch an elastic laminate web transversely to a travel direction in which the web passes between the interengaging rollers, the method comprising the steps of: directing a gas stream carrying dry-ice particles at surfaces of the counterrotating rollers such that the particles free contaminants from surfaces of the rollers; and aspirating freed contaminants and dry-ice particles from immediately adjacent each of the rollers.
 2. The method defined in claim 1, wherein each of the webs rotates in a respective rotation direction and each of the rollers has an inner side engaged with the inner side of the other roller and an outer side, gas streams carrying the dry-ice particles impinging the outer sides of the respective rollers, the contaminants and dry-ice particles being aspirated from the outer sides of the rollers downstream in the rotation direction of the respective roller from the respective nozzle.
 3. The method defined in claim 1, wherein the gas streams are projected from respective nozzles, the method further comprising the step of: reciprocating the nozzles parallel to rotation axes of the rollers back and forth along the counterrotating rollers.
 4. The method defined in claim 3, wherein the freed contaminants and dry-ice particles are aspirated through ports extending generally a full axial length of each of the rollers.
 5. The method defined in claim 1, wherein the carrier-gas stream is at a temperature below the freezing temperature of carbon-dioxide and gaseous carbon dioxide is added to the carrier-gas stream to form the particles.
 6. The method defined in claim 1, wherein the formations of each roller consist of radially outwardly projecting ridges alternating with radially outwardly open grooves, the ridges of each roller engaging in the grooves of the other roller.
 7. In combination with an apparatus having a pair of counterrotating rollers having surface formations that interengage and that stretch a laminate web transversely to a travel direction in which the web passes between the interengaging rollers, means for directing a gas stream carrying dry-ice particles at surfaces of the counterrotating rollers such that the particles free contaminants from surfaces of the rollers; and means juxtaposed with the rollers for aspirating freed contaminants and dry-ice particles.
 8. The apparatus defined in claim 7, wherein each of the webs rotates in a respective rotation direction and each of the rollers has an inner side engaged with the inner side of the other roller and an outer side, the means for directing including respective nozzles aimed at the outer sides of the respective rollers, the means for aspirating including respective suction ports juxtaposed with the outer sides of the rollers downstream in the rotation direction of the respective roller from the respective nozzle.
 9. The apparatus defined in claim 7, wherein the means for directing includes respective nozzles directed at the rollers.
 10. The apparatus defined in claim 9, further comprising actuator means for reciprocating each of the nozzles along the respective roller parallel to a rotation axis of the respective roller.
 11. The apparatus defined in claim 10, wherein the means for aspirating means includes respective suction ports open radially inwardly immediately adjacent each of the rollers and extending generally a full axial length of each of the rollers.
 12. The apparatus defined in claim 7 wherein the means for directing includes a source of the supercold carrier gas and means for mixing gaseous carbon dioxide with the supercold carrier gas to form the dry-ice particles.
 13. The method defined in claim 7, wherein the formations of each roller consist of radially outwardly projecting ridges alternating with radially outwardly open grooves, the ridges of each roller engaging in the grooves of the other roller. 